Permanent magnet bulk degausser

ABSTRACT

One or more pairs of magnet assemblages ( 14  and  16 ) are provided with magnetized segments ( 21 - 30 ) arranged in a Halbach-like array. The magnet assemblages ( 14  and  16 ) define a gap ( 18 ) through which magnetic data storage media ( 12 ) pass in a direction ( 20 ) across the segments ( 21 - 30 ). The magnetized sides ( 36 ) of the magnet assemblages ( 14  and  16 ) face each other thereby creating strong magnetic fields which degauss the magnetic data storage media ( 12 ) passing through the gap ( 18 ).

FIELD OF THE INVENTION

This invention relates generally to magnetic degaussers and moreparticularly to permanent magnet magnetic degaussers for erasingmagnetic data storage devices.

BACKGROUND

Magnetic degaussing systems of various kinds are known in the art.Typically, magnetic fields of varying strength and direction are appliedto the item to be degaussed forcing the magnetization within the objectto change thereby destroying any patterns therein. Magnetic degaussingsystems have become increasingly important with the increasing use ofmagnetic data storage. Data stored magnetically can remain on thestorage medium for long periods of time after its use. For example, acomputer disk's data can be retrieved even after a user has “erased” thedata from the disk because the old data will not be changed until newdata is written over that segment of the disk. If another person were toobtain the disk, that person may be able to access information from thatdisk.

In the art of bulk degaussing of magnetic data storage media,electrically powered degaussing systems are commonly used. For example,laminated steel cores of extruded “U” shapes in association withelectrical windings are generally recognized as one configurationsuitable for erasure of magnetic data storage media. Similarly, “E”shaped cores may be used. Pairs of such cores are often configuredopposite each other with like poles facing, although single sided andoffset configurations are also known in the art. Although suchconfigurations are suitable for some situations, these systems have thedisadvantage of needing a power source to create the fields necessaryfor magnetic data storage media erasure.

More recently, the discovery and improvement of rare earth permanentmagnets have made the generation of magnetic fields of strengthssuitable for bulk media erasure using permanent magnets practical. Suchpermanent magnets can be arranged with steel elements into magneticcircuits that act much like their electric counterparts. The weightrequirements of permanent magnet systems are about equal to the electricsystems. Further, the zero power input required by permanent magnetsoffsets higher production costs as compared to electric systems.

Another advantage of permanent magnet systems includes the use ofindividual elements, which may be off-the-shelf items, rather thantrying to fabricate large elements or permanently magnetizing a singlelarge shape. For example, it is known that a total of eight 2-inch by2-inch by 1-inch neodymium-iron-boron (NeFeB) blocks, magnetized in the1-inch direction, can be adhered by magnetic attraction onto steelplates as groups of four blocks thereby forming two 2-inch by 8-inchpoles, a classic “U” shape magnet of 8-inch depth. Two such “U” shapescan be configured with like poles facing in repulsion across a gapsuited to passage of 1-inch thick magnetic media. Such an assemblage canapply a magnetic field with good uniformity and at least 6000 gauss toevery point in a common form factor for magnetic data storage mediapassing through that field. It is understood that at least a secondpassage of a magnetic storage medium through the field with a differentorientation between the storage medium and the magnetic field isnecessary to impart the desired change within the storage medium toaffect magnetic data storage erasure.

Despite the advantages of these known permanent magnet systems, certaindrawbacks exist. For instance, magnetic data storage media are beingdeveloped with increasing magnetic coercivities such that much strongerfields must be applied to completely erase the media. As such, the 6000gauss strength achieved by known permanent magnet bulk degaussingsystems is marginal with respect to the emerging media's coercivities.

Attempts to increase the strength of the known permanent magnet bulkdegaussing systems by scaling up the systems, however, quickly lead todiminishing returns. Such scaling of prior art includes stackingoff-the-shelf elements in their direction of magnetization, placingelements side by side on the steel plates, stacking and placingelements, or substituting larger custom-made elements or magnets for theoff-the-shelf elements. It is generally recognized in the art of bulkdegaussing that worst case field strength drives performance and that ameasure of nonuniformity in field strength can be tolerated. It is alsoknown that attempts to furnish field strengths sufficient for erasure ofmagnetic storage media with higher coercivities using various prior artfacing “U” arrangements would require at least a correspondinglyincreased amount of NeFeB or other magnetic material plus thick steelcomponents needed to complete the required magnetic circuit. Such asystem would result in an unacceptable degree of field strengthnonuniformity across the gap. In particular, the diminishing returnsfrom prior art scaling using NeFeB elements arise due to flux leakagefrom NeFeB elements to each other and into the steel plates where mediacannot be placed to affect erasure.

Additionally, any such scaling results in larger volume, increasedweight, and greater cost. It is well known that in the assembly of theprior art permanent magnet systems, regions of both magnetic attractionand magnetic repulsion will arise between various elements and members.For example, magnets are attracted to steel plates and to each otherwhen stacked with unlike poles facing. Conversely, placing magnetsadjacent to each other with the same magnetic direction causesrepulsion, as does placing like poles facing each other across a gap. Tocounter such forces, framework members must be added. In the priordevices, a thick steel plate serves a dual role as a required componentof the magnetic circuit and as one of the framework members, but othermembers generally must be of nonmagnetic materials to avoid undesirablemagnetic circuit paths or unnecessary magnetic field fringing effects.In particular, prior devices require an attraction-countering memberbetween unlike poles, which experiences extreme compressive force, andthis member cannot be magnetic steel. These structural requirements onlybecome aggravated with the scaling of the prior permanent magnetdevices.

BRIEF DESCRIPTION OF THE DRAWINGS

The above needs are at least partially met through provision of thepermanent magnet bulk degausser described in the following detaileddescription, particularly when studied in conjunction with the drawings,wherein:

FIG. 1 is a perspective view of a permanent magnet bulk degausserembodying features of the present invention;

FIG. 2 is a side plan view of a Halbach array of square cross-sectionpermanent magnet elements with directions of magnetizations shown byarrows;

FIG. 3 is a perspective view of a preferred permanent magnet element;

FIG. 4 a is a side plan view of a model of the magnetic fields createdby a pair of magnet assemblages in accordance with the array of FIG. 2;

FIG. 4 b is a side plan view of a model of the magnetic fields createdby the pair of magnet assemblages illustrated in FIG. 1;

FIG. 5 a is a graph showing the magnetic flux density along the gapbetween a pair of magnet assemblages in accordance with FIG. 4 a;

FIG. 5 b is a graph showing the magnetic flux density along the gapbetween a pair of magnet assemblages in accordance with FIG. 4 b;

FIG. 6 is a perspective view of an alternate permanent magnet bulkdegausser embodying features of the present invention;

FIG. 7 is a perspective view of a prior art permanent magnet bulkdegausser;

FIG. 8 is a side plan view of an alternate permanent magnet bulkdegausser embodying features of the present invention;

FIG. 9 is a perspective view of a frame structure for use with variousembodiments of the permanent magnet bulk degausser;

FIG. 10 is a side plan view of the frame structure of FIG. 9;

FIG. 11 is a side plan view of an alternate permanent magnet bulkdegausser embodying features of the present invention;

FIG. 12 is a side plan view of a model of the magnetic fields created bythe pair of magnet assemblages illustrated in FIG. 11; and

FIG. 13 is a top plan view of an alternate permanent magnet bulkdegausser embodying features of the present invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will also be understoodthat the terms and expressions used herein have the ordinary meaning asis accorded to such terms and expressions with respect to theircorresponding respective areas of inquiry and study except wherespecific meanings have otherwise been set forth herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to FIG. 1, there is illustrated a permanent magnet bulkdegausser 10 for erasing magnetic storage media 12. The apparatus 10includes a pair of magnet assemblages 14 and 16 arranged so as to definea gap 18 through which magnetic storage media 12 passes in the directionas indicated by arrow 20 across each segment 21-25 and 26-30 of theassemblages 14 and 16. By moving in this direction 20, the magnetic datastorage medium 12 passes through the magnetic field created by themagnet assemblages 14 and 16 thereby facilitating erasure of data on themedium 12. One should note that the magnetic data storage medium 12 canbe any medium including magnetic tape, computer disks, hard drives, andthe like.

The segments 21-25 and 26-30 are aligned adjacently within each magnetassemblage 14 and 16 with the direction of magnetization of eachsuccessive segment rotated by approximately 90 degrees relative to theprevious segment. More specifically, the direction of magnetizationacross successive segments rotates in the same direction so that thedirection of magnetization repeats within a magnet assemblage only everyfifth segment. This magnetization arrangement is commonly known as aHalbach array. In a variation on the traditional Halbach array, segments22 and 24 of magnet assemblage 14 with directions of magnetizationapproximately perpendicular to the gap 18 have two rows of permanentmagnets, whereas segments 21, 23, and 25 with directions ofmagnetization approximately parallel to the gap 18 have one row ofpermanent magnets.

The traditional Halbach array ascribed to Klaus Halbach, asconventionally illustrated in two dimensions in FIG. 2, includes alinear sequence of adjacent squares 31-35 magnetized such that thedirection of magnetization in each adjacent square rotates 90 degreeswith respect to its neighbor, with the direction of rotation constantfrom element to element. The arrows designate a direction ofmagnetization pointing from magnetic South to magnetic North; however,this convention may be reversed without affecting performance as long asthe convention is uniformly applied within a given embodiment. TheHalbach array arrangement forms a strongly magnetic side 36. Neglectingslight imperfections in dimension, shape, and magnetization, side 38 islargely self-shielding and nonmagnetic. Such linear arrays can beillustrated as an unlimited sequence, and the square elementconstruction shown in FIG. 2 typically yields a substantially sinusoidalmagnetic field strength along the direction of the array on the magneticside 36 of the array. As such, the magnet assemblages 14 and 16 of FIG.1 are arranged with the magnetic side of each assemblage facing the gap18.

Preferably each segment 21-30 includes a plurality of permanent magnetsarranged in at least one row such that each permanent magnet in thesegment has a direction of magnetization pointing in the same direction,substantially perpendicular to the length of the row. The preferredpermanent magnet element 40 as illustrated in FIG. 3 is a readilyavailable NeFeB block such as a 2-inch square by 1-inch thick block witha direction of magnetization (as indicated in the figures by an arrow)in the direction of the block's thickness. Such a magnetization producesa magnetic North pole on one 2-inch square face of the block and amagnetic South pole on the opposite 2-inch square face. Neglectingfringing effects at the ends, each preferred permanent magnet generatesa 2-inch wide field in the magnetized direction. Placing additionalpreferred permanent magnets in a row will provide 4-inch, 6-inch, and soon wide fields. As is the case with prior devices, one additionaladjacent magnet suffices to counter fringing effects.

One should understand that in three dimensions, such elements orsegments depicted as having a square cross section may be square plates,cubes, or rods. Similarly, other permanent magnetic materials may beused. For example, SmCo blocks have aspect characteristics similar toNeFeB and can substitute for it. Also, a particular element size is notnecessary. For instance, various segments 21-25 or 26-30 within a magnetassemblage 14 or 16 may have varying sizes and/or shapes. Alternatively,each segment can be an integral permanent magnet with a magnetization ina direction substantially perpendicular to the segment's longestdimension. Also, a complex fixture could magnetize a single large blockinto a one-piece magnet assemblage with several differently magnetizedsegments of the block.

Additionally, it is understood that assembling the invention fromindividual blocks can introduce acceptable minor field imperfections dueto surface roughness, size and shape tolerance, and the common practiceof plating NeFeB material. Similarly, introduction of thin nonmagneticelements such as shims between permanent magnet elements 40 or segments21-25 or 26-30 may introduce some acceptable field imperfections.Likewise, relatively thin and magnetically soft ferromagnetic materialsintroduced as shims between permanent magnet elements 40 or segments21-25 or 26-30 would hardly disturb the fields.

FIGS. 4 a and 4 b model the magnetic flux vectors of two embodimentswhere the magnet assemblages are arranged in repulsion across the gap18. For objective comparisons, all models disclosed herein use residualflux density (B_(r)) of 10,000 gauss. One skilled in the art willrecognize that NeFeB grades are available with B_(r) exceeding 13,000gauss. FIG. 4 a demonstrates the magnetic flux for an embodiment using atraditional Halbach array as illustrated in FIG. 2 with square segmentcross-sections. FIG. 4 b models the magnetic flux for the preferredembodiment non-traditional Halbach array as illustrated in FIG. 1. Forboth embodiments, magnetic flux concentrates within the gap 18, andminimal magnetic flux is present outside the gap 18.

FIG. 5 a illustrates a spatial waveform derived from the internal fieldof the magnet assemblage pair of FIG. 4 a. It can be seen that thewaveform of FIG. 5 a approximates a “windowed” sinusoid. FIG. 5 billustrates a spatial waveform derived from the internal field of thepreferred embodiment model of FIG. 4 b. It can be seen that the waveformof FIG. 5 b has a distinctively triangular characteristic when comparedto the waveform of FIG. 5 a.

The harmonic content above the fundamental as seen in FIG. 5 b may bedetrimental to some Halbach applications, such as for particle beamaccelerator components. Peak strength, however, is paramount in the artof erasing magnetic media, and the harmonic content of the numericanalysis given in FIG. 5 indicates a 4% stronger field, nearly a 10,000gauss peak magnetic field, for the preferred embodiment non-traditionalHalbach array when compared to the traditional Halbach array embodiment.By contrast, prior art magnetic circuits, such as illustrated in FIG. 7,generate only about half this strength, and scaling of the prior artmagnetic circuit shown in FIG. 7 by adding additional permanent magnetsfails to achieve the field strengths of the embodiments of the inventionwhile using a comparable amount of NeFeB. For example, doubling theNeFeB material in either of two dimensions of the prior permanent magnetdegausser of FIG. 7 increases the magnetic strength from about half thatof the embodiments of FIGS. 4 a and 4 b to about 70% of that strength.Doubling NeFeB in both dimensions of the prior art degausser uses morematerial than a non-traditional Halbach embodiment but has severalpercent less field strength.

Alternatively, Halbach-like arrays of more or less than five segmentscan be utilized. For example, a mirror-imaged pair of three-segment (asillustrated in FIG. 6) or five-segment (as illustrated in FIG. 1)assemblages with magnetic sides facing in repulsion creates fields muchlike the prior art permanent magnet facing “U” arrangements (asillustrated in FIG. 7), but each embodiment offers respectivelyimproving degrees of uniformity of field. Simulations indicate that thethree-segment arrangement of FIG. 6 nearly doubles the field strength ofthe prior permanent magnet arrangement of FIG. 7. A seven-segmentarrangement not only doubles the prior arrangement's strength, but alsoproduces two magnetic fields of equal strength and opposite directionalong a media path 20.

In one such alternative embodiment illustrated at FIG. 6, as few asthree segments 64, 65, and 66 can be arranged within a magnet assemblage62 in a configuration not generally recognized as a complete Halbacharray, but still effective for erasing magnet data storage media. Themagnet assemblages 60 and 62 of FIG. 6 each have magnetic sides facingtoward the gap 18 through which magnetic data storage medium 12 passes.The segments 64-66 of magnet assemblage 62 line up across the gap 18from the segments 67-69 of magnet assemblage 60 such that the directionsof magnetization of segments 64-66 mirror the directions ofmagnetization of segments 67-69 in what is known as an arrangement inrepulsion.

The alternative embodiment of FIG. 6, if built using the preferredpermanent magnet, saves 28% on material cost and weight as compared tothe embodiment of FIG. 1. Although the alternative embodiment of FIG. 6also includes less field strength per unit gap width and slightly lessuniformity across the gap, such an embodiment could be applied, forexample, with a narrower gap 18 to achieve higher strength for futureand continually smaller varieties of magnetic storage media.

In addition to the field strength and uniformity advantages of thevarious embodiments, there is much less need for steel elements andframing materials when compared to prior permanent magnet devices.Contrary to the prior permanent magnet devices, steel is not requiredfor any supporting members or magnetic circuit elements. Also, any suchshielding of the small magnetic flux leakage of the various embodimentswould only be needed for certain applications such as against compassinterference in airborne or other mobile applications. Typically, thinsteel also suffices to shield against the slight magnetic flux leakagesarising from imperfections in magnet element dimensions andmagnetization. In applications where shielding is not a factor,nonmagnetic materials having better strength to weight characteristicscan alternatively be used for framing. Additionally, the repulsive orattractive forces between the magnet assemblages of the variousembodiments are generally reduced in comparison to prior conventionaldegaussers. Thus, less extensive framing support is needed.

In alternative embodiments, the overall size of the degausser 10 can bemanipulated. For instance, a data processing operation that depends onerasing a large quantity of microminiaturized hard disk drives couldbenefit from a drastically scaled down version of the invention. In oneexample, it is now feasible to issue a personal digital assistant (PDA)for each patient entering a hospital. Also, each PDA may include anapparatus for removeably connecting an inexpensive 5 mm thick 4G Bytedisk drive. The PDA could conveniently accompany a patient anywhere inthe hospital (except places like MRI imagers) to capture all diagnosticand treatment information on the one drive. Medical records by law,however, must be protected. Thus, by using a physically smallerembodiment of the invention, such small drives can be erased after theiruse by being passed through the degausser 10. The large variety of NeFeBblocks available off the shelf other than the preferred permanentmagnets raises many possibilities for configurations of the invention.

Also, Halbach arrays are known with magnetization angles of less than 90degrees between segments. Use of multiple thin plate magnet segmentswith such reduced angular magnetization yield some further optimizationfor certain applications. Such approaches trade off some loss atadditional contact surfaces between segments for improved harmoniccontent of the magnetic field profile.

In yet another embodiment, a pair of mirror-imaged permanent magnetassemblages 80 and 82 as illustrated in FIG. 8 can be offset from eachother by various degrees, generating a magnetic field component in thedirection across the gap 18. By varying the offset, a variety ofmagnetic field directions are produced within the gap 18. Offsetembodiments of the invention can address various directional erasurecharacteristics such as perpendicular recording on hard disk drives.

In still another embodiment, gap adjustability can be introduced totrade off field strength against media thickness capacity. Framestructures for manipulating the magnet assemblages to adjust the gapwidth and to offset the assemblages are known, and an example of such aframe structure 90 is illustrated in FIGS. 9 and 10. Lower plate 92supports lower magnet assemblage 16. Upper plate 94 supports uppermagnet assemblage 14. Pillars 96 are rigidly affixed to lower plate 92by any conventional method. The pillars 96 include a thick diametermid-section 98 between upper magnet assemblage 14 and lower magnetassemblage 16, a smaller diameter upper portion 100 that slip fitsthrough apertures defined (not shown) by upper plate 94, and a thickdiameter top portion 102 fixedly attached to smaller diameter upperportion 100. The thick diameter mid-section 98 and top portion 102 ofthe pillars 96 define the limits of the adjustability of the gap 18.Rods 104 attach to lower plate 92 in a known manner allowing the rods104 to rotate within and pull on lower plate 92. At least upper portions106 of rods 104 have screw threads over the range of adjustability thatmate with threaded holes (not shown) defined by upper plate 94.

Crank 108 and lower pinion gear 110 rigidly attach to each other androtatably attach to upper plate 94. Lower spur gears 112 and tall upperpinion gears 114 also rigidly attach to each other and rotatably attachto upper plate 94. Upper spur gears 116 attach rigidly to the partiallythreaded rods 104. Turning crank 108 causes lower pinion gear 110 toturn lower spur gears 112 that turn tall upper pinion gears 114, therebycausing upper spur gears 116 and rods 104 to turn. Threaded portions 106of rods 104 act on upper plate 94 to selectively raise or lower it, thusaffecting the gap 18 between magnet assemblages 14 and 16 for thepassage of various magnetic storage media with different thicknesses.

The form of gap adjustment shown in FIGS. 9 and 10 is illustrative andnot limiting. Similar adjustment apparatuses can be provided for otherembodiments of the invention, such as offset forms, attractive forms,and multiple assemblage pairs set at angles to a media path. The variousforms of the invention can be combined with each other and with priorart along a media path, with or without a gap adjustment apparatus.

Similarly, many prior art applications may be used with the variousembodiments to impart the sufficient exposure of the magnetic storagemedia to varying fields necessary to accomplish complete erasure. Asnoted above, when trying to erase magnetic storage media, simplyproviding a simple linear media path through a single magnetic fielddirection is generally recognized as requiring further media-fieldvariation, such as two passes through the magnetic field combined with arotation of the media or field. Such actions can be performed by a humanoperator, or by the use of mechanisms known in the art. Also, variousmechanisms can impart a raster-scan-like motion to the magnetic mediapath to accomplish full magnetic exposure of media volume to a smallermagnetic field volume.

Alternatively, two or more pairs of permanent magnet assemblages canprovide fields of varying direction along a media path 20. In oneembodiment, one pair of magnet assemblages is mirror-imaged across thegap with magnetic sides in repulsion such as the degausser in FIG. 1forming fields generally in the direction parallel to the gap 18, andanother pair has elements arranged so the magnetic sides are inattraction such as the degausser in FIG. 11 forming two fields generallyin opposite directions across the gap 18. FIG. 11 illustrates a pair ofmagnet assemblages 118 and 120 arranged in attraction using a basicpermanent magnet element with a direction of magnetization differentfrom that of the preferred magnet element. Like the embodiments of FIG.1 and FIG. 6, the arrangement illustrated in FIG. 11 can be modified ina number ways including adding or removing segments or by building thepair of assemblages with alternative permanent magnet elements.

FIG. 12 models magnetic flux vectors for the pair of assemblages 118 and120 in attraction illustrated in FIG. 11 showing strong flux projectingacross the gap 18. The assemblages 118 and 120 are also largelynon-magnetic and self-shielding outside the gap 18. It can be seen thatthe pair of five segment assemblages 118 and 120 produces two fields ofopposite direction within gap 18. The strength of each field peaks near10,000 gauss, which, like the assemblage pairs arranged in repulsion,constitutes a significant advance beyond the results achievable withprior magnetic circuits. Passage of magnetic storage media 12 through amagnet assemblage pair arranged in attraction before or after passagethrough a magnet assemblage pair arranged in repulsion provides theexposure to varying fields necessary for erasure of certain varieties ofmagnetic storage media.

In yet another embodiment illustrated in FIG. 13, two pairs of magnetassemblages 122 and 124 with magnetic sides in repulsion, each of depthapproximately 1.4 times an intermediate dimension of the magneticstorage media 12 size, are provided along a media path 20 and orientedwith field directions at 45 degree angles to that path and at 90 degreesto each other forming a “one pass” configuration sufficient to erase themagnetic storage media with one pass through the magnet assemblages.Such placement reduces the effective width of the field across the pathto approximately 70% of the width achieved in embodiments like FIG. 1 orFIG. 6. Unlike those embodiments, the embodiment of FIG. 13 need onlytreat media 12 with a single pass in the orientation shown with longestdimension aligned in direction of motion 20. The magnetic fielddirection varies by 90 degrees with along the path 20 through the twopairs of assemblages 122 and 124. Embodiments with a single pair ofassemblages generally require two passes, including one pass with theorientation indicated in FIG. 1 and FIG. 6 with longest dimension ofmedia 12 perpendicular to direction 20 to media motion. It can beappreciated that media placement limits 126 reside well clear of theends of pairs of assemblages 122 and 124 where fringing effects weakenthe field strength.

This embodiment can be further modified to add cross-gap magneticfields, forming a “universal” configuration that erases horizontal andperpendicular hard disk drive media in one pass and no media rotation.For example, to the configuration of FIG. 13 can be added the cross-gapfield direction of an array pair with magnetic faces in attraction likethat of FIG. 11, forming a “universal” configuration that eraseshorizontal and perpendicular hard disk drive media in one pass and nomedia rotation. One should note that not all elements of suchmulti-gapped embodiments need be Halbach-like arrays.

Those skilled in the art will recognize that a wide variety ofmodifications, alterations, and combinations can be made with respect tothe above described embodiments without departing from the spirit andscope of the invention, and that such modifications, alterations, andcombinations are to be viewed as being within the ambit of the inventiveconcept.

1. An apparatus for erasing magnetic storage media comprising: at leastone pair of magnet assemblages; each magnet assemblage comprising atleast three segments; each segment having a direction of magnetizationapproximately perpendicular to the longest dimension of the segment; atleast one magnet assemblage arranged such that the segments are alignedadjacently with the direction of magnetization of each successivesegment rotated by approximately 90 degrees relative to the previoussegment wherein the direction of magnetization for a segment repeatsevery fifth segment if the magnet assemblage includes five or moresegments; and a gap defined by each pair of magnet assemblages such thata magnetic field created by each assemblage exists at least partially inthe gap.
 2. The apparatus of claim 1 wherein at least one segment is anintegral piece.
 3. The apparatus of claim 1 wherein at least one segmentcomprises a plurality of permanent magnets arranged in at least one rowsuch that each permanent magnet in the segment has a direction ofmagnetization pointing in the same direction.
 4. The apparatus of claim3 wherein at least one permanent magnet includes a cross section in theshape of a square and a height that is one half of a length of a side ofthe square with the direction of magnetization in the direction of theheight of the permanent magnet.
 5. The apparatus of claim 3 wherein atleast one permanent magnet is a neodymium-iron-boron block.
 6. Theapparatus of claim 3 wherein the direction of magnetization for eachsegment is either approximately perpendicular to or approximatelyparallel to the gap and each segment with a direction of magnetizationsubstantially perpendicular to the gap includes at least two rows ofpermanent magnets and each segment with a direction of magnetizationsubstantially parallel to the gap includes fewer rows of permanentmagnets than the segments with a direction of magnetizationsubstantially perpendicular to the gap.
 7. The apparatus of claim 1wherein the direction of magnetization for each segment is obliquerelative to the gap.
 8. The apparatus of claim 7 wherein at least onepair of magnet assemblages is aligned such that segments from eachmagnet assemblage line up across the gap and that each segment mirrorsthe direction of magnetization of the segment directly across the gap.9. The apparatus of claim 1 wherein the direction of magnetization forat least one segment is either approximately perpendicular to orapproximately parallel to the gap.
 10. The apparatus of claim 9 whereineach pair of magnet assemblages includes the same number of segments.11. The apparatus of claim 10 wherein each pair of magnet assemblages isaligned such that segments from each magnet assemblage line up acrossthe gap and that each segment mirrors the direction of magnetization ofthe segment directly across the gap.
 12. The apparatus of claim 10wherein each pair of magnet assemblages is aligned such that segmentsfrom each magnet assemblage line up across the gap and that each segmentwith a direction of magnetization approximately perpendicular to the gappoints in approximately the same direction as the segment across thegap.
 13. The apparatus of claim 10 wherein at least one pair of magnetassemblages is aligned such that segments from each magnet assemblageline up across the gap and that each segment mirrors the direction ofmagnetization of the segment directly across the gap, at least one pairof magnet assemblages is aligned such that segments from each magnetassemblage line up across the gap and that each segment with a directionof magnetization approximately perpendicular to the gap points inapproximately the same direction as the segment across the gap, and thegaps for each pair of magnet assemblages line up such that magneticmedia storage may pass directly from one gap to the other.
 14. Theapparatus of claim 1 wherein at least one pair of magnet assemblages isaligned such that segments from at least one magnet assemblage areoffset relative to the segments across the gap.
 15. The apparatus ofclaim 1 wherein at least one magnet assemblage comprises a Halbach arrayacross the segments.
 16. The apparatus of claim 1 further comprising anadjustable frame structure securing the magnet assemblages such that thewidth of the gap between the magnet assemblages can be adjusted.
 17. Theapparatus of claim 1 further comprising a lateral adjustable framestructure securing the magnet assemblages such that the lateral positionof the magnet assemblages can be adjusted.
 18. The apparatus of claim 1wherein the two magnet assemblages of at least one pair of magnetassemblages have different numbers of segments.
 19. An apparatus forerasing magnetic storage media comprising: at least two pairs of magnetassemblages; each magnet assemblage comprising at least three segments;each segment having a direction of magnetization approximatelyperpendicular to the longest dimension of the segment; each magnetassemblage arranged such that the segments are aligned adjacently withthe direction of magnetization of each successive segment rotated byapproximately 90 degrees relative to the previous segment wherein thedirection of magnetization for a segment repeats every fifth segment ifthe magnet assemblage includes five or more segments; a gap defined byeach pair of magnet assemblages such that a magnetic field created byeach assemblage exists at least partially in the gap; and at least oneof the at least two pairs of magnet assemblages arranged with thesegments of the first magnet assemblage aligned at 90 degrees relativeto the segments of the second magnet assemblage and with the segments ofboth magnet assemblages at a 45 degree angle relative to a magneticstorage media path through each gap defined by each pair of magnetassemblages.
 20. The apparatus of claim 19 wherein the at least one ofthe at least two pairs of magnet assemblages are further arranged suchthat each of the magnet assemblages are arranged in repulsion.
 21. Theapparatus of claim 19 further comprising: at least one additional pairof magnet assemblages disposed on the magnetic storage media path; eachmagnet assemblage of the at least one additional pair comprising atleast three segments; each segment of the magnet assemblages of the atleast one additional pair having a direction of magnetizationapproximately perpendicular to the longest dimension of the segment;each magnet assemblage of the at least one additional pair arranged suchthat the segments are aligned adjacently with the direction ofmagnetization of each successive segment rotated by approximately 90degrees relative to the previous segment wherein the direction ofmagnetization for a segment repeats every fifth segment if the magnetassemblage includes five or more segments; and the at least oneadditional pair of magnet assemblages arranged in attraction.